Fully-filled telephone cable with improved screen

ABSTRACT

A fully-filled telephone cable comprising a core including a plurality of insulated wires surrounded by a composite screening tape of aluminum foil having a layer of insulating material on and bonded to at least one surface thereof, the screen being indented at longitudinally spaced intervals so as to provide circumferentially extending and continuous contact with the core to thereby restrict fluid flow when the screen is pierced to the pierced portion intermediate the pair of longitudinally spaced indentations at the ends of such portion.

United States Patent [191 Ferrentino 1 1 FULLY-FILLED TELEPHONE CABLE WITH IMPROVED SCREEN [75] Inventor: Antonio Ferrentino, Monza, Italy [73] Assignee: Industrie Pirelli Societa per Azioni,

Milan, Italy [22] Filed: May 2, I974 [21 Appl. No.: 466,177

[30] Foreign Application Priority Data May 23, 1973 Italy 24440/73 [52] US. Cl. 174/102 D; 174/23 R [51] Int. Cl. H0lb 7/18 [58] Field of Search. 174/23 R, 23 C, 116, 102 D,

[56] References Cited UNITED STATES PATENTS Nicolas 174/102 D Priaroggia 174/102 D [4 1 May 20, 1975 3,71 1,621 1/1973 .lachimowicz 174/106 D 3,766,309 10/1973 Calzolari........... 174/102 D 3,767,454 10/1973 Franke, Jr 174/23 R UX Primary Examiner-Arthur T. Grimley Attorney, Agent, or Firm-Brooks Haidt Haffner & Delahunty [57] ABSTRACT A fully-filled telephone cable comprising a core including a plurality of insulated wires surrounded by a composite screening tape of aluminum foil having a layer of insulating material on and bonded to at least one surface thereof, the screen being indented at longitudinally spaced intervals so as to provide circumferentially extending and continuous contact with the core to thereby restrict fluid flow when the screen is pierced to the pierced portion intermediate the pair of longitudinally spaced indentations at the ends of such portion.

5 Claims, 2 Drawing Figures FULLY-FILLED TELEPHONE CABLE WITH IMPROVED SCREEN The present invention relates to improvements in the sealing of metallic screens of fully-filled telephone cables in order to increase the adherence between the screen and the core and consequently to prevent the propagation of moisture in longitudinal direction in said cables.

As is known, a fully-filled cable has a considerable tightness against the percolation of water or other polluting fluids which may penetrate inside thereof in consequence of damage to the sheath. Said tightness is obtained by filling the free spaces existing between the elements of the core with a filling material, comprising, in general, solid or semi-solid gels obtained from mineral oil. As is known, the core is a bunch of conductors formed by grouping together individual, appropiately insulated conductors, or pairs, quads, trefoils and so on, the latter being constituted by stranding individually insulated wires.

The core is wrapped, in turn, with tapes of insulating material, usually impregnated papers, and, in some embodiments, is covered with a screen constituted by a smooth metallic tape longitudinally applied in the shape of a tube, which tape, for reasons of flexibility of the cable, must be bonded to an outer plastic sheath. The tape is of the composite type, that is, it comprises a layer of metal foil having a layer of insulation on its outer surface only or a layer of insulation on both its inner and outer surfaces. For example, it may consist of polyethylene on aluminum foil, aluminum foil between polyethylene layers, aluminum foil with a layer of polyethylene on one surface and a layer of polyester resin on its other surface, etc. Generally, by means of the usual application techniques, it is not possible to obtain perfect adherence between the tube which forms the screen and the underlying core or its wrapping. ln fact, in general, it is not possible to clamp the metallic tube on the core by means of the external plastic sheath, exploiting the shrinkage of the latter during cooling, because of the relevant thickness of the screening tapes (of the order of tenths of a millimeter). Even ifa preliminary closure of the metallic tube is carried out by thermally welding its overlapping edges, unsatisfactory results are obtained, due to the difficulty of clamping the tape and carrying out the thermal welding of its edges on cores which have not an absolutely constant diameter.

Resort has then been had to the system of applying the filling material on the wrappings of insulating material wound up on the core before applying the metallic tape constituting the screen. Said filling material, although it reduces the empty space between the screen and the core, has, however, small adhesion to the inner surface of the composite tape, and moreover, it can cause drawbacks due to outflowing of the filling material at the edge to be thermally welded. Consequently, attempts have been made to apply the screen by thermally welding its edge and then, to bring said screen into contact with the core, pushing the former transversely and circumferentially on the latter, by means of polygonal sealing corrugations inscribed in a circumference whose diameter is smaller than the diameter of the screen. Even if, in this case, one reaches an improved result, said polygonal corrugations have the disadvantage that there are corners where the tape of the screen is not in contact with the wrappings of the core. From a theoretical point of view, said corners should be filled with the filling material, but in practice, they frequently are empty and, therefore, they facilitate an undesirable, longitudinal flow of liquids.

The present invention has, as one object, the elimination of the hereinbefore-mentioned disadvantages by providing a fully-filled, telephone cable provided with a screen which has corrugations or spaced indentations which are devoid of corners, and consequently of a circular type, in which the inner surface of said screen is in contact, without being longitudinally continuous, with the underlying wrappings, along a circumferential region which is circular in cross-section, so that any longitudinal flow of moisture is prevented.

More precisely, the principal object of the present invention is a telephone cable of the fully-filled type, provided with a screen formed by a composite longitudinal tape and provided with corrugations or indentations which bring the inner surface of the screen into contact with the wrappings of the core, such corrugations being circumferential and circular in crosssection.

ln a preferred embodiment of the invention, a telephone cable of the fully-filled type, having a screen formed by a longitudinal composite tape, is provided with sealing corrugations or indentations which bring the inner surface of said screen into contact with the wrappings of the core, said circumferential corrugations being disposed relative to one another so as to form a plurality of groups situated at the same mutual distance in axial direction and each group comprising at least a first plurality of equal segmental corrugations, equally spaced from one another in circumferential direction. Each segmental corrugation corresponds to an arc of a circle, the inner diameter of which is substantially equal to the outer diameter of said wrapping. Each group also comprises a second plurality of segmental corrugations equal to said first plurality, but angularly rotated with respect to it, so that a portion of each end of each of its segmental corrugations is respectively adjacent in the axial direction to a corresponding portion of a first and of a second segmental corrugation of said first plurality, the latter being circumferentially consecutive to each other.

The attached sheet of drawing represents diagrammatically, by way of example, a practical embodiment of the fully-filled telephone cable provided with a corrugated screen improved according to the invention, and in the drawing:

FIG. 1 is a perspective view of a preferred embodiment in which a telephone cable core is surrounded by a screen; and

FIG. 2 is an enlarged, cross-sectional view of the embodiment in FlG. l and is taken along the line 2-2 indicated in FIG. 1.

FIGS. 1 and 2 illustrate a cable of the fully-filled type, constituted by a core 10 of insulated conductors with insulating wrappings 11, the latter preferably being made of crepe paper of the type normally used in telephone cables. Both the core 10 and the wrappings 11 are impregnated with a filling material, for example, a gel obtained from mineral oil, and are surrounded by the screen 12. As used in the claims set forth hereinafter, the word core is intended to include a group of insulated conductors either with or without the wrappings 11 or a similar insulating layer.

The screen 12 preferably comprises a composite tape of the type described hereinbefore, and FIGS. 1 and 2 illustrate a composite tape having an inner layer 120 of aluminum, an outer layer 12b of a synthetic resin, such as polyethylene, bonded to the layer 12a and an inner layer 12c of a synthetic resin, such as polyethylene or a polyester, bonded to the layer 120. The screen tape 12 is longitudinally folded around the core and with its longitudinal edges 19, 20 bonded together by thermal welding or in another known manner.

The screen 12 is provided with the groups 13 of circumferential corrugations or indentations equally spaced apart from one another in the axial direction of the cable. Each group 13 comprises at least a first plurality 14 of segmental corrugations equal to one another and equally spaced apart in the circumferential direction, each segmental corrugation corresponding to an arc of a circle whose inner diameter, namely, the diameter measured by starting from the tape surface in contact with the wrappings 11, is equal to the outer diameter of the wrappings 11 and subtends an angle at the center, preferably smaller than 90, since, the greater the number of segmental corrugations, the better the tightness. Each group 13 also comprises a second plurality 15 of segmental corrugations, equal to the first plurality and adjacent to the latter, but angularly rotated with respect to it so that a portion of each end 16 and 17 of each segmental corrugation 18 is respectively adjacent in the axial direction, namely, in the direction of the cable axis, and overlapping a corresponding portion of a segmental corrugation 21 and of a second segmental corrugation 22 of said first plurality 14, circumferentially consecutive to each other. It will be noted that such arrangement of the indentations provides a tube inner surface portion at each group of indentations which is re-entrant and which is in continuous circumferential engagement with the exterior surface of the core and its wrappings.

In the embodiment illustrated, the segmental corrugations have a sector shape, but it is clear that they could have any other shape which will cause the screen 12 to engage the wrappings 11 without leaving empty spaces which extend a substantial distance longitudinally of the cable and which will thereby ensure a good tightness in the longitudinal direction.

In the event that water (or any other polluting liquid) should percolate through a leak between two consecutive groups 13 of circumferential corrugations, such water or liquid cannot propagate beyond the short space defined by said groups, since each group of circumferential corrugations constitutes a re-entrant, continuous contact belt between the inner surface of the screen 12 and the wrappings 11, so that any longitudinal migration of the liquid is prevented.

Although a preferred embodiment of the present invention has been described and illustrated, it will be understood by those skilled in the art that various modifications may be made without departing from the principles of the invention.

What is claimed is:

l. A telephone cable comprising a core including a plurality of insulated conductors surrounded by a composite tape folded longitudinally around said core to thereby form a tube of said tape around said core, said tape comprising a layer of metal having a layer of synthetic resin on and bonded to at least the outwardly facing surface of said layer of metal, said tube being indented at each of a plurality of longitudinally spaced positions with a plurality of indentations extending circumferentially of said core, the sum of the circumferential lengths of said indentations being at least equal to the circumference of said core, each of said indentations having an inner surface conforming to the exterior surface of said core and having a circumferential length less than the circumference of said core, at least one of said indentations at each of said positions being longitudinally and circumferentially displaced with respect to, but longitudinally adjacent, at least one other of said indentations at said last-mentioned position and said indentations at each position being disposed around said core with each so-displaced indentation overlapping at least one other indentation and with the inner surface of each so-displaced indentation forming a continuation of the inner surface of the adjacent indentation to provide substantially circumferentially continuous engagement of the inner surfaces of said indentations with the exterior surface of said core at each said position whereby said core is encircled at longitudinally spaced positions by a circumferentially extending, re-entrant tube inner surface portion which is in substantially continuous engagement with said core.

2. A telephone cable as set forth in claim 1, further comprising a filler material within said tube and filling the spaces within said tube and said core.

3. A telephone cable as set forth in claim 1, wherein said core comprises a wrapping of insulating tape around said conductors and intermediate said conductors and said tape.

4. A telephone cable as set forth in claim 1, wherein each of said plurality of circumferentially extending indentations at each of said positions has an inner surface in the shape of an arc of a circle having a diameter substantially equal to the outer diameter of said core, said plurality of indentations at each said position are in two longitudinally spaced but adjacent groups with the indentations in each group circumferentially spaced from each other, with the indentations of one group circumferentially displaced with respect to the indentations of the other group, with the ends of each indentation of one group overlapping the ends of a pair of circumferentially successive indentations of the other group and with the inner surfaces of said ends of each indentation of said one group forming a continuation of the inner surfaces of said ends of said pair of successive identations of said other group.

5. A telephone cable as set forth in claim 4, wherein said arc of a circle subtends an angle less than 

1. A telephone cable comprising a core including a plurality of insulated conductors surrounded by a composite tape folded longitudinally around said core to thereby form a tube of said tape around said core, said tape comprising a layer of metal having a layer of synthetic resin on and bonded to at least the outwardly facing surface of said layer of metal, said tube being indented at each of a plurality of longitudinally spaced positions with a plurality of indentations extending circumferentially of said core, the sum of the circumferential lengths of said indentations being at least equal to the circumference of said core, each of said indentations having an inner surface conforming to the exterior surface of said core and having a circumferential length less than the circumference of said core, at least one of said indentations at each of said positions beIng longitudinally and circumferentially displaced with respect to, but longitudinally adjacent, at least one other of said indentations at said last-mentioned position and said indentations at each position being disposed around said core with each so-displaced indentation overlapping at least one other indentation and with the inner surface of each so-displaced indentation forming a continuation of the inner surface of the adjacent indentation to provide substantially circumferentially continuous engagement of the inner surfaces of said indentations with the exterior surface of said core at each said position whereby said core is encircled at longitudinally spaced positions by a circumferentially extending, re-entrant tube inner surface portion which is in substantially continuous engagement with said core.
 2. A telephone cable as set forth in claim 1, further comprising a filler material within said tube and filling the spaces within said tube and said core.
 3. A telephone cable as set forth in claim 1, wherein said core comprises a wrapping of insulating tape around said conductors and intermediate said conductors and said tape.
 4. A telephone cable as set forth in claim 1, wherein each of said plurality of circumferentially extending indentations at each of said positions has an inner surface in the shape of an arc of a circle having a diameter substantially equal to the outer diameter of said core, said plurality of indentations at each said position are in two longitudinally spaced but adjacent groups with the indentations in each group circumferentially spaced from each other, with the indentations of one group circumferentially displaced with respect to the indentations of the other group, with the ends of each indentation of one group overlapping the ends of a pair of circumferentially successive indentations of the other group and with the inner surfaces of said ends of each indentation of said one group forming a continuation of the inner surfaces of said ends of said pair of successive identations of said other group.
 5. A telephone cable as set forth in claim 4, wherein said arc of a circle subtends an angle less than 90*. 